In The Media > Trying to make exercise a stop-start affair


2 Aug 2012

You do not have to train like an Olympic athlete to keep fit. In fact, new studies show that 10-minute bouts of exercise can help lower blood pressure.

''Every four years, the Olympics get people excited to exercise,'' says a professor of exercise, Glenn Gaesser, at Arizona State University. He has supervised a study about exercise and high blood pressure that was inspired in part by the London Games.

The streets and gyms fill with people who, fuelled by stories of Olympic success, ''run or work out for an hour or more,'' Gaesser says.

But he says that within weeks, most people have quit and resumed their sedentary lives. ''We wanted to see if there were approaches to exercise that would fit more easily into people's lifestyles, but still be effective'' in improving health, he says.

So he and his colleagues gathered a group of adult volunteers. Each volunteer was generally healthy except for early symptoms of high blood pressure, a condition called prehypertension.

High blood pressure is one of the primary risk factors for heart disease and stroke, and prehypertension is one of the primary risk factors for full-blown high blood pressure. Symptoms include an average daily blood pressure approaching 140/90 millimetres of mercury and a tendency for blood pressure to reach dangerous levels throughout the day.

Prehypertension is known to respond well to exercise. But many studies of exercise and blood pressure have employed moderate exercise sessions lasting about 30 minutes a day, which is the commonly recommended standard for improving health.

Gaesser, however, asked his volunteers to walk briskly at an intensity equal to about 75 per cent of their maximum heart rate for 10 minutes, three times during a day. The sessions took place at 9.30am, 1.30pm and 5.30pm.

On another day, the volunteers completed one 30-minute supervised session of brisk walking in the mid-afternoon, while on the final day, they did no exercise.

All of them wore cuffs that monitored blood pressure continuously for a day at a time. As it turned out, exercise was helpful in controlling blood pressure, but breaking up the workout into three short sessions was significantly more effective than the single half-hour session. ''The fractionised exercise led to lower average 24-hour blood pressure readings,'' Gaesser says.

It also resulted in lower blood pressure ''load,'' or the number of times during the day when a volunteer's blood pressure spiked above 140/90. Lowering blood pressure load is important, Gaesser says, because a high load can indicate that someone with prehypertension is likely to progress to full-blown high blood pressure.

Overall, the results ''are really encouraging,'' he says. ''For people who think that 30 minutes of exercise is too hard or takes up too much time, we can say just do 10 minutes, three times during the day.'' Conversely, if someone was tempted to dismiss 10 minutes of walking as too meagre to be meaningful, he says, at least for blood pressure control, fractionised exercise is more effective than a single 30-minute bout.

His work joins a small but compelling body of science suggesting that, for many purposes, short, cumulative exercise sessions are beneficial.

A study published last year in PLoS One found that in children and teenagers, repeated bouts of running or other physical activity lasting as little as five minutes at a time reduced their risks of poor cholesterol profiles, wide waistlines and above-average blood pressure readings as much as longer exercise sessions did.

Other studies have found that exercising sporadically throughout the day helps weight control, particularly for older women. It also, in a few small studies, improved aerobic fitness among previously sedentary people as much as a single, longer workout did and, as a regimen, was more likely to be maintained.

But fractionised exercise has its limits. ''You're not going to make it to the Olympics,'' Gaesser said.


 

Gretchen Reynolds